Fluorocarbon based solvents have been used extensively for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils. In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent leaves the object free of residue. This is contrasted with liquid solvents which leave deposits on the object after rinsing.
A vapor degreaser is used for difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently. The conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al., in U.S. Pat. No. 3,085,918 disclose a suitable vapor degreaser comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with cloths soaked in solvents and allowed to air dry.
The art has looked towards azeotropic compositions including the desired fluorocarbon components such as trichlorotrifluoroethane, which include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse cleaning. Thus, the vapor degreasing system acts as a still. Therefore, unless the solvent composition is essentially constant boiling, (i.e., is an azeotrope or azeotrope-like) fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. For example, preferential evaporation of the more volatile components of the solvent mixtures would result in mixtures with changed compositions which may have less desirable properties, like lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity (this would be the case if the mixture was not an azeotrope or azeotrope-like).
The art is continually seeking new fluorocarbon based azeotrope mixtures or azeotrope-like mixtures which offer alternatives for new and special cleaning applications for vapor degreasing and other cleaning applications. Currently, fluorocarbon based azeotrope-like mixtures are of particular interest because they are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter have been implicated in causing environmental problems associated with the depletion of the earth's protective ozone layer.
Accordingly, it is an object of the present invention to provide novel environmentally acceptable azeotropic compositions which are useful in a variety of industrial cleaning applications.
It is another object of the invention to provide azeotrope-like compositions which are liquid at room temperature and which will not fractionate under conditions of use.
Other objects and advantages of the invention will become apparent from the following description.